Molecular evidence of anteroposterior patterning in adult echinoderms.

The origin of the pentaradial body plan of echinoderms from a bilateral ancestor is one of the most enduring zoological puzzles1,2. Because echinoderms are defined by morphological novelty, even the most basic axial comparisons with their bilaterian relatives are problematic. To revisit this classical question, we used conserved anteroposterior axial molecular markers to determine whether the highly derived adult body plan of echinoderms masks underlying patterning similarities with other deuterostomes. We investigated the expression of a suite of conserved transcription factors with well-established roles in the establishment of anteroposterior polarity in deuterostomes3-5 and other bilaterians6-8 using RNA tomography and in situ hybridization in the sea star Patiria miniata. The relative spatial expression of these markers in P. miniata ambulacral ectoderm shows similarity with other deuterostomes, with the midline of each ray representing the most anterior territory and the most lateral parts exhibiting a more posterior identity. Strikingly, there is no ectodermal territory in the sea star that expresses the characteristic bilaterian trunk genetic patterning programme. This finding suggests that from the perspective of ectoderm patterning, echinoderms are mostly head-like animals and provides a developmental rationale for the re-evaluation of the events that led to the evolution of the derived adult body plan of echinoderms.

DGGE-based detection method for Quahog Parasite Unknown (QPX).

Quahog Parasite Unknown (QPX) is a significant cause of hard clam Mercenaria mercenaria mortality along the northeast coast of the United States. It infects both wild and cultured clams, often annually in plots that are heavily farmed. Subclinically infected clams can be identified by histological examination of the mantle tissue, but there is currently no method available to monitor the presence of QPX in the environment. Here, we report on a polymerase chain reaction (PCR)-based method that will facilitate the detection of QPX in natural samples and seed clams. With our method, between 10 and 100 QPX cells can be detected in 1 l of water, 1 g of sediment and 100 mg of clam tissue. Denaturing gradient gel electrophoresis (DGGE) is used to establish whether the PCR products are the same as those in the control QPX culture. We used the method to screen 100 seed clams of 15 mm, and found that 10 to 12% of the clams were positive for the presence of the QPX organism. This method represents a reliable and sensitive procedure for screening both environmental samples and potentially contaminated small clams.

The Culture, Sexual and Asexual Reproduction, and Growth of the Sea Anemone Nematostella vectensis.

Nematostella vectensis, a widely distributed, burrowing sea anemone, was raised through successive sexual generations at room temperature in non-circulating seawater. It has separate sexes and also reproduces asexually by transverse fission. Cultures of animals were fed Artemia sp. nauplii every second day. Every eight days the culture water was changed, and the anemones were fed pieces of Mytilus spp. tissue. This led to regular spawning by both sexes at eight-day intervals. The cultures remained reproductive throughout the year. Upon spawning, adults release either eggs embedded in a gelatinous mucoid mass, or free-swimming sperm. In one experiment, 12 female isolated clonemates and 12 male isolated clonemates were maintained on the 8-day spawning schedule for almost 8 months. Of the female spawnings, 75% occurred on the day following mussel feeding and water change, and 64% of the male spawnings were similarly synchronized under this regime. Fertilization and development occur when gametes from both sexes are combined in vitro. At 20°C, the embryos gastrulate within 12-15 hours. Spherical ciliated planulae emerge from egg massess 36-48 hours post-fertilization. The planulae elongate and form the first mesenteric couple, as well as four tentacle buds, by day five. By day seven, they metamorphose and settle as 250-500 µm long, four-tentacled juvenile anemones. More tentacles and all eight macrocnemes are present at 2-3 weeks. Individuals may become reproductively mature in as few as 69 days. Nematostella vectensis has the potential to become an important model for use in cnidarian developmental research.